A variety of mechanical heart valve prostheses have been developed which operate hemodynamically, in conjunction with the pumping action of the heart, to take the place of a defective natural valve. These valves include constructions having valve members in the form of a single occluder, a pair of occluders or three or more occluders; however, to date, heart valves of the bileaflet type have generally been the preferred mechanical heart valves.
U.S. Pat. No. 4,276,658 to Hanson et al. discloses a bileaflet heart valve made of pyrocarbon-coated graphite which has been sold in the United States for over a decade.
U.S. Pat. No. 4,689,046 to Bokros shows another similar bileaflet heart valve design wherein a pair of flat leaflets have straight mating edges which mate with each other at the center of the valve and have arcuate edges that seat against the interior circular cylindrical wall of the valve body.
U.S. Pat. No. 4,451,937 to Klawitter discloses heart valves wherein flat occluders and occluders of complex curvature are guided by ears that travel in arcuate recesses and pivot upon pairs of upper and lower protuberances which end radially inward from the wall of the valve body. In the closed positions in some of the valves, a pair of leaflets are oriented generally perpendicular to the centerline of the valve body and the tips of the leaflets abut midpoint stops that extend inward from the valve body interior wall. Similar single occluder valve constructions are also shown.
U.S. Pat. No. 5,123,920 to Bokros shows a bileaflet heart valve having leaflets that are aerodynamically shaped and that have rectilinear surfaces which are curved in a direction parallel to the pivot axes.
U.S. Pat. No. 5,152,785 to Bokros et al. shows a bileaflet heart valve having leaflets that are flat and leaflets that are curved in a direction generally parallel to the centerline axis through the valve when the leaflets are in the open position.
U.S. Pat. No. 5,171,263 to Boyer et al. shows a bileaflet heart valve having leaflets that are curved in a direction parallel to the pivot axes and which contact an abutment extending radially inward from the valve body interior wall to define the closed position.
U.S. Pat. No. 5,314,467 to Shu shows a bileaflet heart valve having leaflets of complex curvature.
U.S. Pat. No. 5,354,330 to Hanson et al. shows a bileaflet heart valve of this general type having flat leaflets which rotate on spherical pivots and have circular edges which seat against the interior surface of the valve body.
U.S. Pat. No. 5,376,111 to Bokros et al. shows bileaflet and single occluder valves where the occluders may be flat or curved.
U.S. Pat. No. 5,641,324 to Bokros et al. shows an improved bileaflet heart valve of this general type having a novel valve body entrance and a novel pivot mechanism. The disclosures of all these U.S. patents are incorporated herein by reference.
The more that such mechanical prosthetic valves have been studied, the more that investigators have concluded that the ideal prosthetic valve simply does not yet exist. From a materials standpoint, pyrolytic carbon has been determined to be adequately nonthrombogenic; as a result, the problem of combatting thrombosis in mechanical valves is presently felt to lie in preventing excess turbulence, high shear stresses, cavitation and local regions of stasis. Blood is a very delicate tissue, and even minor abuses caused by cavitation, turbulence and high shear stress can cause either hemolysis, thrombosis and/or emboli generation at local regions of stagnation. Cavitation in regions near surfaces of the structural components can cause erosion that, if serious, can lead to valve failure. Therefore, it is felt that future improvement in the characteristic of thromboresistance in mechanical valves will likely be attained through the achievement of smooth, nonturbulent flow and the absence of cavitation and stasis.
The search continues for improved mechanical heart valve prostheses that provide passageways through which blood will flow freely and with a minimum of drag in the open position, which will close quickly without cavitation or significant noise upon the occurrence of backflow to minimize regurgitation of blood, and which can be efficiently manufactured and assembled. Accordingly, new valve designs incorporating such features have continued to be sought.